This invention relates to a process of fabricating cathode-ray tubes and particularly to a process for forming cathodoluminescent screens and apertured color selection electrodes in such tubes.
Cathode-ray tubes for use in color television usually include a cathodoluminescent screen of red, green and blue emitting phosphor lines or dots, electron gun means for exciting the screen, and an apertured mask interposed between the gun means and the screen. The apertured mask is a thin metal sheet precisely disposed adjacent to the screen so that the mask apertures are systematically related to the phosphor lines or dots.
Presently, cathode-ray tubes utilizing color selection techniques that require an apertured mask are generally manufactured employing the practice of pairing. This means that a finish-fabricated apertured mask is paired with a faceplate panel and is used as a patterned master during formation of a screen on the faceplate. After screen formation, the mask is incorporated into the tube to serve its color selection function.
The method of pairing, although it generally produces a commercially acceptable tube, has several disadvantages. Formation of a screen requires the insertion and removal of the mask several times. During each such insertion and removal, the chances of denting or otherwise damaging the mask are relatively high. Additionally, there is also a possibility that the mask will not reset properly in the panel. Furthermore, in a negative tolerance matrix shadow mask type tube or in a focus mask tube wherein the size of the electron-excited screen areas are smaller than their associated apertures, other problems may be encountered. For example, in one method for forming such tubes, a mask used as a patterned master to form a screen is reetched to enlarge its apertures. During a second etch there is the possibility of either damaging the mask or over etching it. Such occurrences result in a faceplate that must be totally rescreened utilizing a different mask.
Therefore, there is a need for tube construction methods that minimize the amount of manual handling and, if possible, permit the use of replaceable color selection electrodes without the need for rescreening a tube.